On Thursday, the U.S. Food and Drug Administration (FDA) announced that women should be taking only half the currently prescribed dose of the sleep aid, Ambien (zolpidem).

Laboratory studies and driving tests have confirmed what some users have long complained about: they feel drowsy the morning after taking sleep medication, The New York Times noted. Drowsiness can contribute to car accidents, a concern for the morning commute or when driving children to school. The FDA’s new dosage recommendation focuses particularly on women because new research reveals that it takes women longer than men to metabolize the drug, The New York Times reports. Eight hours after taking a sleeping pill, an estimated 10 to 15 percent of women will have a level of zolpidem–the active ingredient in Ambien–in their blood that could impair driving, where only about 3 percent of men will.

Sleeping pills are widely prescribed in the United States. IMS, a health care information and technology company, says that 60 million sleeping pill prescriptions were written in 2011, about 40 million for products containing zolpidem. Sleeping pill users have long reported troubling side effects associated with the medication, including activities–sleepwalking, middle of the night eating–for which they have no memory the next day. According to the Times, doctors say they’ve had numerous reports from patients of morning drowsiness, car accidents, and near misses, and they wonder why it took so long for the FDA to fully investigate.

The FDA said it was difficult to make a direct connection between sleeping pill use and drowsy driving until the agency compared driving simulation results with data on levels of zolpidem in the blood. A level above 50 nanograms per milliliter increases the risk of a crash, said Dr. Ellis Unger of the FDA’s Center for Drug Evaluation and Research, according to The New York Times.

The FDA recommends reducing the dose of Ambien, Edluar, Zolpimist, and similar medications from 10 milligrams to 5 milligrams for women. Men should consult their doctors about the appropriate dose, said The New York Times.